Generally, as semiconductor devices become more highly integrated, performing fabrication processes gets more difficult. For instance, in a MOS transistor, as a gate/source/drain electrode is reduced in size, the length of a channel is reduced as well. As the channel length is reduced, a thickness of a gate insulating layer is reduced as well, reducing the mobility of electrons.
Moreover, as the concentration of channel impurities rises, flicker noise increases to affect analog signal characteristics. Therefore, in manufacturing semiconductor devices for SoC (system on chip) technology, it is difficult to ensure reliability of operation. The flicker noise is a sort of intrinsic noise in an active device. As flicker noise is inversely proportional to frequency, it may be called ‘1/f noise’. The flicker noise rapidly increases on a low frequency band. The flicker noise is associated with electron mobility, channel impurity and the like. In an SoC for a stable radio frequency signal, the flicker noise may cause a serious problem.